Isoxazoles with nootropic activity

ABSTRACT

PCT No. PCT/EP88/00445 Sec. 371 Date Mar. 20, 1989 Sec. 102(e) Date Mar. 20, 1989 PCT Filed May 19, 1988 PCT Pub. No. WO88/09330 PCT Pub. Date Dec. 1, 1988.Nootropically active isoxazoles which are certain specified derivatives of N-(5-isoxazolecarbonyl)-4 aminobutyric acid.

The present invention relates to compounds with nootropic activity and,more particularly, it relates to derivatives ofN-(5-isox-azolecarbonyl)-4-aminobutyric acid, the processes for theirpreparation, their therapeutic use and the pharmaceutical compositionscontaining them as active ingredient.

Piracetam, 2-pyrrolidinoneacetamide (Merck Index, X edition, page 1080,no. 7363) is a compound described in Belgian Pat. No. 667906 (UnionChimique Belge) as central stimulant.

For its action at cerebral level on glucose metabolism as well as,especially, in increasing acetylcholine release, Piracetam is consideredthe parent compound of nootropic drugs and it is used in therapy in thetreatment of cerebral efficiency disorders, particularly in elderlypatients.

Piracetam, even if it is used in therapy, shows a relativeeffectiveness.

In order to improve the therapeutic activity of the parent compoundseveral different compounds have been prepared.

Among these we can mention, for example, the derivatives of1-benzoyl-2-pyrrolidinone described in European Pat. No. 5143(Hoffmann-La Roche) and, particularly, the derivative known asAniracetam, 1-(4-methoxy-benzoyl)-2-pyrrolidinone (USAN and the USPDictionary of Drug Names 1987, page 30).

It is worth noting, however, that, as far as we know, the compounds withnootropic activity developed up to now do not contain an isoxazole ringand furthermore most of them have a remarkable structural analogy withthe parent compound Piracetam.

Besides, as can be seen also in Aniracetam, the pyrrolidinone ringremains present, as peculiar characteristic.

We have surprisingly found and they are the object of the presentinvention, compounds of formula ##STR1## wherein

n represents a number selected from 1 and 2;

R represents a hydrogen atom, a halogen atom, hydroxy, a C₁ -C₆ alkyl oralkoxy;

R₁ represents hydroxy, an optionally unsaturated C₁ -C₁₈ alkoxy or an##STR2## group;

R₂ and R₃, the same or different, represent a hydrogen atom, a linear orbranched C₁ -C₆ alkyl, a group of formula (CH₂)_(m) R₄ wherein

m represents an integer selected from 1, 2 ,and 3;

R₄ represents a carboxy group, an alkoxycarbonyl group having from 1 to6 carbon atoms in the alkoxy moiety or a group of formula ##STR3##

R₅ and R₆, the same or different, represent a hydrogen atom or a linearor branched C₁ -C₆ alkyl;

or one of R₂ and R₃ represents a group of formula ##STR4## wherein R₄has the above reported meanings and R₇ represents a linear or branchedC₁ -C₄ alkyl optionally substituted by phenyl, hydroxy or by a mercaptogroup; and the other represents a hydrogen atom;

or, in addition, R₂ and R₃, together with the nitrogen atom to whichthey are bonded, form a 5, 6 or 7 membered heterocycle which may furthercontain 1 or 2 heteroatoms selected among nitrogen, oxygen and sulphur.

Specific examples are 1-pyrrolidinyl, 1-piperazinyl,4-methyl-1-piperazinyl, 1-piperidyl and 1-pyrrolidinyl-2-one.

A further object of the present invention are the salts of the compoundsof formula I, which have an acidic function, with pharmaceuticallyacceptable organic or inorganic bases and the salts of the compounds offormula I, wherein R₁ contains a basic function, with organic orinorganic acids suitable for pharmaceutical use.

Examples of organic or inorganic bases useful as salifying agents aresodium or potassium hydroxides, ammonium hydroxide, lysine, arginine,cysteine and 2-amino-2-hydroxymethyl-1,3-propanediol. Examples oforganic or inorganic acids useful as salifying agents are hydrochloricacid, hydrobromic acid, sulfuric acid, tartaric acid, citric acid andglutamic acid.

The compounds of formula I, object of the present invention, havenootropic activity.

Examples of compounds comprised in formula I are the following: ##STR5##wherein R has the above reported meanings but preferably it represents achlorine or bromine atom, hydroxy, methoxy or ethoxy, methyl or ethyl.

The preparation of the compounds of formula I is another object of thepresent invention and comprises a condensation reaction between achloride of 5-isoxazolecarboxylic acid of formula ##STR6## wherein

R has the above reported meanings, and 4-aminobutyric acid or aderivative thereof of formula

    H--(NH--CH.sub.2 --CH.sub.2 --CH.sub.2 --CO).sub.n --R.sub.1(II-A)

wherein

n and R₁ have the above reported meanings, in an inert solvent in thepresence of an acceptor of halogenhydric acids.

Examples of suitable acceptors of halogenhydric acids are inorganic ororganic bases such as sodium hydroxide or carbonate, triethylamine,N-methyl-morpholine and pyridine.

The reaction of compounds II with 4-aminobutyric acid (II-A n=1 R₁ =OH)gives the compounds of formula I wherein n=1 and R₁ =OH. Such compoundsare transformed into their reactive derivatives such as mixed anhydridesand, without any isolation, they are condensed with 4-aminobutyric acidgiving the compounds of formula I wherein n=2 and R₁ =OH. For greatersimplicity the compounds of formula I wherein R₁ =OH will be indicatedhereinafter as compound I-a) ##STR7## The compounds of formula I whereinR₁ is alkoxy are prepared from compounds Ia by esterification.

The esterification reaction is carried out with saturated or unsaturatedaliphatic alcohols such as methanol, ethanol, propanol, butanol, cetylicalcohol, linolenic alcohol or stearic alcohol, in the presence ofcatalytic amounts of an inorganic acid.

The preparation of compounds I wherein ##STR8## is carried out byreacting suitable reactive derivatives of compounds Ia with a suitableamino derivative according to the following reaction ##STR9## wherein n,R, R₁, R₂ and R₃ have the above reported meanings and Y represents aleaving group.

Examples of reactive derivatives (III) of the compounds of formula Iaare mixed anhydrides obtainable by reaction with alkylchloroformatessuch as isobutylchloroformate.

Compounds III are, then, reacted, without any isolation, with an aminoderivative of formula IV in a suitable solvent, which may be compound IVitself.

Examples of suitable amino derivatives of formula IV are ammonia, mono-or di-substituted amines such as methylamine, dimethylamine,diethylamine and di-n.propylamine; alkylendiamines such asN,N-diethyl-ethylendiamine and N,N-diisopropyl-ethylendiamine; cyclicderivatives such as pyrrolidine, 2-pyrrolidinone, piperazine andN-methyl-piperazine or natural aminoacids such as glycine, alanine,valine, serine, cysteine, phenylalanine and derivatives thereof.

The compounds of formula I wherein n=1 and the ##STR10## group is a1-pyrrolidinyl-2-one may also be prepared from compounds Ia (n=2) by acyclization reaction.

The cyclization reaction is carried out in one step through theformation of the corresponding acyl halide as intermediate. Thisintermediate, without any isolation, cyclizes in the same reactionenvironment giving the compound I wherein n=1 and ##STR11## is a1-pyrrolidinyl-2-one.

The intermediate acyl halides are prepared by reaction with a suitablehalogenating agents such as thionyl chloride, phosphorus trichloride,phosphorus pentachloride, phosphorus tribromide, phosphoruspentachloride, oxalyl bromide and oxalyl chloride. For economical andpractical reasons only, thionyl chloride is preferably used.

The cyclization reaction is carried out optionally in the presence ofinert organic solvents such as toluene and benzene. It is clear to theman skilled in the art that the compounds of formula I, object of thepresent invention, can be prepared following alternative routes too.

For example the esterification of the carboxyl group can be carried outdirectly on 4-aminobutyric acid or a derivative thereof, that is beforecondensation with compound II.

In a similar way the compounds of formula I wherein ##STR12## can beprepared also according to the following reaction ##STR13## wherein n,R, R₁, R₂ and R₃ have the above reported meanings. According to thismethod, at first, the functionalization of the carboxyl group of4-aminobutric acid or of 4-(4-aminobutyroyl)aminobutyric acid is carriedout in order to obtain the amides of formula V.

These amides are, then, condensed with the acyl chloride of5-isoxazolecarboxylic acid (II), in an inert organic solvent and in thepresence of an acceptor of halogenhydric acids, to give the compounds offormula I wherein ##STR14##

The compounds of formula I are active on central nervous system and theycan be used in pharmaceutical field as nootropics. By the electroshock(ECS) amnesia test, described in example 8, in rat the pharmacologicalactivity of the compounds object of the present invention was evaluatedin comparison with the activity of Piracetam and Aniracetam.

The test results showed that the ED₅₀ values (μmol/kg) of the compoundsof formula I are generally remarkably lower than that of Piracetam andAniracetam.

Particularly, the ED₅₀ values are up to 20 times lower in case of "peros" administration and up to 10 times lower by perfusion than that ofPiracetam.

The compounds of formula I have no toxicological problem. They exhibit acomplete tolerability even when they are administered by perfusion atdose of 2 g/kg.

The therapeutic uses of the compounds object of the present inventionare in the treatment of impairments of cerebral functionality due toageing as well as to pathologic or traumatic reasons such as for exampleamnesia and decrease in cognitive capacity.

The therapeutic dose of the compounds of formula I and of the saltsthereof depends on several factors such as the way of administration,the specific pharmaceutical composition, the treatment needed and theindividual response to the therapy. In general it will be comprisedbetween 5 and 2000 mg/day in one or more administrations.

A further object of the present invention are the pharmaceuticalcompositions containing the compounds of formula I or pharmaceuticallyacceptable salts thereof as active ingredient optionally together withone or more, solid or liquid, organic or inorganic pharmaceuticalexcipients such as diluents, preserving agents, moistening agents,colouring agents, flavouring agents and so on. The pharmaceuticalcompositions object of the present invention can be administered insolid pharmaceutical preparations, such as tablets, coated tablets,capsules, granulates and suppositories or in liquid pharmaceuticalpreparations such as syrups, suspensions, emulsions and solutionssuitable for oral or parenteral administration.

The compounds object of the present invention can be prepared in slowand protracted release pharmaceutical formulations too. Thepharmaceutical compositions object of the present invention may alsocontain the compounds of formula I or pharmaceutically acceptable saltsthereof in association with other active ingredients selected, forexample, among aminoacids, N-acetyl-cysteine, co-enzymes, mineral saltsand vitamins.

The preparation of the pharmaceutical compositions object of the presentinvention is carried out by usual techniques.

In order to better illustrate the present invention, the followingexamples are now given.

EXAMPLE 1 Preparation of N-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyricacid (Compound no. 1)

To a solution of 4-aminobutyric acid (11.34 g; 0.11 mol) and sodiumhydroxide (4.4 g; 0.11 mol) in water (150 ml), cooled at 10° C., asolution of 3-bromo-5-isoxazolecarbonylchloride (21 g; 0.10 mol) intoluene (150 ml) and a solution of sodium hydroxide (4.0 g; 0.10 mol) inwater (150 ml) were added simultaneously. The reaction mixture was keptunder stirring at room temperature for 2 hours. The aqueous layer wasseparated, washed with toluene (150 ml) and acidified with concentratedhydrochloric acid up to pH 2.

The precipitate was extracted three times with ethyl acetate (200 ml).The organic extracts were collected, washed with water and dried onsodium sulphate.

After evaporation of the solvent, the solid crude was cristallized fromacetonitrile (150 ml) givingN-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyric acid (23 g; 83% yield)with m.p. 140°-141° C. ¹ H-NMR (DMSO-d₆): delta (ppm): 1.6-2.1 (2H, m,CH₂ --CH₂ --CH₂); 2.1-2.5 (2H, m, CH₂ CO); 3.33 (2H, q, CH₂ N); 7.39(1H, s, --CH═).

In a similar way the following compounds were prepared.

N-(3-chloro-5-isoxazolecarbonyl)-4-aminobutyric acid (Compound no. 2)

m.p. 140°-141° C. (acetonitrile); 81% yield.

¹ H-NMR (DMSO-d₆): delta (ppm): 1.5-2.1 (2H, m, CH₂ --CH₂ --CH₂);2.1-2.6 (2H, m, CH₂ CO); 3.36 (2H, q, CH₂ N); 7.39 (1H, s, --CH═).

N-(3-methoxy-5-isoxazolecarbonyl)-4-aminobutyric acid (Compound no. 3)

m.p. 134°-135° C. (acetonitrile); 78% yield.

¹ H-NMR (DMSO-d₆): delta (ppm): 1.5-2.1 (2H, m, CH₂ --CH₂ --CH₂);2.1-2.5 (2H, m, CH₂ CO); 3.29 (2H, q, CH₂ N); 3.97 (3H, s, CH₃ O); 6.82(1H, s, --CH═).

N-(3-methyl-5-isoxazolecarbonyl)-4-aminobutyric acid (Compound no. 4)

m.p. 136°-137° C. (acetonitrile); 75% yield. ¹ H-NMR (DMSO-d₆): delta(ppm): 1.5-2.1 (2H, m, CH₂ --CH₂ --CH₂); 2.1-2.5 (2H, m, CH₂ CO); 2.32(3H, s, CH₃); 3.29 (2H, q, CH₂ N); 7.00 (1H, s, --CH═).

N-(3-n.butyl-5-isoxazolecarbonyl)-4-aminobutyric acid (Compound no. 5)

m.p. 130°-131° C. (acetonitrile); 75% yield.

¹ H-NMR (DMSO-d₆): delta (ppm): 0.90 (3H, t, CH₃); 1.32 (2H, m, CH₂--CH₃); 1.61 (2H, m, CH₂ --CH₂ --CH₃); 1.73 (2H, m, CH₂ --CH₂ --CO);2.26 (2H, dd, CH₂ CO); 2.66 (2H, dd, CH₂ --C═); 3.25 (2H, m, N--CH₂);6.96 (1H, s, --CH═); 8.92 (1H, s, NH); 12.12 (1H, s, OH).

N-(5-isoxazolecarbonyl)-4-aminobutyric acid (Compound no. 6) m.p.149°-151° C. (acetonitrile); 64% yield.

¹ H-NMR (DMSO-d₆): delta (ppm): 1.75 (2H, m, CH₂ --CH₂ --CH₂); 2.27 (2H,t, CH₂ CO); 3.27 (2H, dt, N--CH₂); 7.06 (1H, d, --CH═C); 8.74 (1H, d,--CH═N); 8.99 (1H, s, NH); 12.12 (1H, s, OH).

EXAMPLE 2 Preparation of ethylN-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyrate (Compound no. 7)

A suspension of N-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyric acid (10g; 0.036 mol), prepared according to the method described in example 1,in absolute ethanol (300 ml), containing a catalytic amount ofconcentrated H₂ SO₄, was kept under stirring at room temperature for 24hours.

The obtained solution was evaporated to dryness and the solid residuewas dissolved in water (100 ml) and extracted 3 times with ethyl acetate(100 ml).

The organic extracts were collected, washed with water, dried on sodiumsulphate and evaporated.

The solid residue was crystallized from diisopropyl ether (100 ml)obtaining ethyl N-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyrate (9.1 g;83% yield) with m.p. 72°-3° C.

¹ H-NMR (DMSO-d₆): delta (ppm): 1.18 (3H, t, CH₃); 1.5-2.2 (2H, m, CH₂--CH₂ --CH₂); 2.2-2.6 (2H, m, CH₂ CO); 3.32 (2H, q, CH₂ N); 4.08 (2H, q,CH₂ --CH₃); 7.40 (1H, s, --CH═).

EXAMPLE 3N-[4-oxo-4-(1-pyrrolidinyl)butyl]-3-bromo-5-isoxazolecarboxamide(Compound no. 8)

To a solution of N-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyric acid(11.8 g; 0.04 mol), prepared according to the method described inexample 1, and N-methyl-morpholine (4.41 ml; 0.04 mol) in anhydroustetrahydrofuran (260 ml), cooled at -15° C., isobutylchloroformate (5.22ml; 0.04 mol) was slowly added.

After standing under stirring at -10° C. for 15 minutes, a solution ofpyrrolidine (3.30 ml; 0.04 mol) in anhydrous tetrahydrofuran (10 ml) wasadded dropwise to the reaction mixture kept at the same temperature.

At the end of the addition it was kept under stirring for 12 hours atroom temperature.

After evaporation of the solvent, the residue was dissolved inchloroform (150 ml). The solution was washed with HCl 0.1N (50 ml), withwater, with an aqueous solution of K₂ CO₃ and finally several times withwater up to neutral pH.

The organic layer was dried on sodium sulphate and, after evaporation ofthe solvent, the solid residue was crystallized from ethyl acetate (100ml) obtainingN-[4-oxo-4-(1-pyrrolidinyl)butyl]-3-bromo-5-isoxazolecarboxamide (10.9g; 82% yield) with m.p. 120°-121° C.

¹ H-NMR (DMSO-d₆): delta (ppm): 1.5-2.1 [6H, m, CH₂ --CH₂ --CH₂, CH₂--(CH₂)₂ --CH₂ ]; 2.1-2.5 (2H, m, CH₂ CO); 3.1-3.7 (6H, m, CH₂ N, CH₂--N--CH₂); 7.46 (1H, s, --CH═).

In a similar way the following compounds were prepared:

N-[4-(4-methyl-1-piperazinyl)-4oxobutyl]-3-bromo-5-isoxazolecarboxamide(Compound no. 9)

m.p. 124°-125° C. (ethyl acetate); 85% yield.

¹ H-NMR (DMSO-d₆): delta (ppm): 1.5-2.0 (2H, m, CH₂ --CH₂ --CH₂);2.0-2.5 (9H, m, CH₂ CO, ##STR15## 3.1-3.7(6H, m, CH₂ N, ##STR16## 7.36(1H, s, --CH═).

N-[4-[2-(diethylamino)ethylamino]-4oxobutyl]-3-bromo-5-isoxazolecarboxamide(Compound no. 10)

m.p. 80°-82° C. (ethyl acetate); 65% yield.

¹ H-NMR (DMSO-d₆): delta (ppm): 0.93 (6H, t, 2CH₃); 1.5-2.8 [10H, m,(CH₂)₂ CO, CH₂ --N--(CH₂ --CH₃)₂ ]; 2.9-3.5 (4H, m, 2CH₂ N); 7.37 (1H,s, --CH═).

N-[4-[2-(diisopropylamino)ethylamino]-4-oxobutyl]-3-bromo-5-isoxazolecarboxamide(Compound no. 11)

m.p. 81°-83° C. (diisopropyl ether-ethyl acetate); 78% yield.

¹ H-NMR (DMSO-d₆): delta (ppm): 0.96 (12H, d, 4CH₃); 1.5-3.6 (12H, m,5CH₂, 2CH); 7.41 (1H, s, --CH═).

Ethyl N-[N-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyroyl]glicinate(Compound no. 12)

m.p. 72°-73° C. (diisopropyl ether); 88% yield.

¹ H-NMR (DMSO-d₆): delta (ppm): 1.19 (3H, t, CH₃); 1.5-2.1 (2H, m, CH₂--CH₂ --CH₂); 2.1-2.4 (2H, m, CH₂ CO); 3.33 (2H, q, CH₂ --CH₂ --N); 3.87(2H, d, N--CH₂ --CO); 4.16 (2H, q, CH₂ --CH₃); 7.46 (1H, s, --CH═).

EthylN-[N-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyroyl]-4-aminobutyrate(Compound No. 13)

m.p. 121°-122° C. (ethyl acetate); 89% yield.

¹ H-NMR (DMSO-d₆): delta (ppm): 1.18 (3H, t, CH₃); 1.5-2.6 (8H, m, 2CH₂--CH₂ CO); 2.8-3.6 (4H, m, 2CH₂ N); 4.09 (2H, q, CH₂ CH₃); 7.39 (1H, s,--CH═).

4-[N-(3-bromo-5-isoxazolecarbonyl)-amino]-butyramide (Compound no. 14)

m.p. 178°-179° C. (ethanol); 61% yield

¹ H-NMR (DMSO-d₆): delta (ppm): 1.72 (2H, m, CH₂ --CH₂ --CH₂); 2.09 (2H,dd, CH₂ CO); 3.24 (2H, m, N--CH₂); 6.78 (1H, s, H--N--H); 7.29 (1H, s,H--N--H); 7.34 (1H, s, --CH═); 9.06 (1H, t, NH--CH₂).

4-[[N-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyroyl]-amino]-butyramide(Compound no. 15)

m.p. 202°-204° C. (dimethylformamide); 72% yield.

¹ H-NMR (DMSO-d₆): delta (ppm): 1.58-1.73 (4H, m, 2CH₂ --CH₂ --CH₂);2.03 (2H, dd, CH₂ CONH₂); 2.10 (2H, dd, CH₂ --CONH); 3.01-3.23 (4H, m,2NHCH₂); 6.73 (1H, s, H--N--H); 7.25 (1H, s, H--N--H); 7.34 (1H, s,--CH═); 7.82-9.06 (2H, s, 2CONH).

n.hexyl N-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyrate (Compound no.16)

m.p. 52°-54° C. (hexane); 44% yield.

¹ H-NMR (DMSO-d₆): delta (ppm): 0.86 (3H, t, CH₃); 1.2-1.3 [6H, m,(CH₂)₃ CH₃ ]; 1.5-1.6 (2H, m, OCH₂ --CH₂); 1.77 (2H, m, CH₂ --CH₂ --CO);2.36 (2H, t, CH₂ CO); 3.28 (2H, m, N--CH₂); 3.99 (2H, t, OCH₂); 7.35(1H, s, --CH═); 9.07 (1H, t, NH).

1-[N-[N-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyroyl]-4-aminobutyroyl]pyrrolidine(Compound no. 17)

m.p. 157°-159° C. (dimethylformamide); 53% yield.

¹ H-NMR (DMSO-d₆): delta (ppm): 1.5-1.9 (8H, m, 4CH₂); 2.10 (2H, dd, CH₂CO); 2.21 (2H, dd, CH₂ CO); 3.04 (2H, m, NHCH₂); 3.2-3.4 (6H, m, 3CH₂N); 7.35 (1H, s, --CH═); 7.83 (1H, t, CONH); 9.06 (1H, t, CONH).

EXAMPLE 4 Preparation ofN-[4-(di-n.propylamino)-4-oxobutyl]-3-bromo-5-isoxazolecarboxamide(Compound no. 18)

A solution of 3-bromo-5-isoxazolecarbonyl chloride (2.95 g; 0.014 mol)in methylene chloride (5 ml) was added dropwise to a solution, cooled at5° C., of 4-aminobutyric acid di-n.propylamide (2.60 g; 0.014 mol) andtriethylamine (1.95 ml; 0.014 mol) in methylene chloride (52 ml).

At the end of the addition the reaction mixture was kept under stirringfor 6 hours at room temperature and then it was extracted with HCl 0.1N(20 ml), with water, with a saturated aqueous solution of NaHCO₃ (20 ml)and finally with water up to neutral pH.

The organic layer was dried on sodium sulphate and, after evaporation ofthe solvent, the solid residue was crystallized from diisopropylether.

N-[4-(di-n.propylamino)-4-oxobutyl]-3-bromo-5-isoxazolecarboxamide (3.6g; 71% yield) was obtained with m.p. 78°-79° C.

¹ H-NMR (DMSO-d₆): delta (ppm): 0.82 (6H, t, 2CH₃); 1.1-2.1 (6H, m, 2CH₂CH₃, CH₂ --CH₂ --CH₂); 2.1-2.5 (2H, m, CH₂ CO); 3.0-3.5 (6H, m, CH₂ NH,2CH₂ N); 7.33 (1H, s, --CH═).

EXAMPLE 5 Preparation ofN-[N-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyroyl]-4-aminobutyric acid(Compound no. 19) Method A

To a solution of ethylN-[N-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyroyl]-4-aminobutyrate(23.6 g; 0.061 mol), prepared according to the method described inexample 3, in methanol (236 ml), cooled at 10° C., a solution of sodiumhydroxide (2.64 g; 0.065 mol) in water (60 ml) was added dropwise.

At the end of the addition, it was kept under stirring at roomtemperature for 18 hours.

After evaporation of most solvent, the solution was diluted with water(200 ml) and extracted twice with chloroform (50 ml). The aqueous layerwas acidified to pH 2 with HCl at 10%. The precipitate was filtered,washed with water up to neutral pH and it was crystallized fromisopropanol (200 ml).

N-[N-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyroyl]-4-aminobutyric acidwas obtained (20.8 g; 94% yield) with m.p. 157°-158° C.

¹ H-NMR (DMSO-d₆): delta (ppm): 1.4-2.5 (8H, m, 2CH₂ --CH₂ --CO);2.8-3.6 (4H, m, 2CH₂ N); 7.37 (1H, s, --CH═).

In a similar way the following compound was prepared.

N-[N-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyroyl]glycine (Compound no.20)

m.p. 187°-189° C. (isopropanol); 91% yield.

¹ H-NMR (DMSO-d₆): delta (ppm): 1.5-2.0 (2H, m, CH₂ --CH₂ --CH₂);2.0-2.5 (2H, m, CH₂ --CH₂ --CO); 3.0-3.6 (2H, m, CH₂ --CH₂ N); 3.80 (2H,d, CH₂ COO); 7.43 (1H, s, --CH═).

Method B

To a solution of N-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyric acid(69.27 g; 0.25 mol), prepared according to the method described inexample 1, and triethylamine (34.80 ml; 0.25 mol) in anhydroustetrahydrofuran (700 ml), cooled at --15° C., isobutylchloroformate(32.67 ml; 0.25 mol) was added slowly.

After stirring at -10° C. for 15 minutes, a solution of 4-aminobutyricacid (30.94 g; 0.30 mol) and triethylamine (41.76 ml; 0.30 mol) in water(190 ml) and dimethylformamide (60 ml) was added dropwise keeping thereaction mixture at the same temperature.

After stirring at room temperature for 3 hours, the solvent w evaporatedand the residue was dissolved in water (350 ml). The obtained aqueoussolution was acidified with HCl at 10% and the precipitate was filtered,washed with water up to neutral pH and it was crystallized fromisopropanol (600 ml).

N-[N-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyroyl]-4-aminobutyric acidwas obtained (55.5 g; 61% yield) with m.p. 157°-158° C.

EXAMPLE 6 Preparation of1-[N-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyroyl]-2-pyrrolidinone(Compound no. 21)

A solution of1-[N-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyroyl]-4-aminobutyric acid(9.0 g; 0.0025 mol), prepared according to the method described inexample 5, and thionyl chloride (2.72 ml; 0.0375 mol) in toluene (250ml) was heated under reflux for 15 minutes.

After cooling and evaporation of the solvent, the solid residue wascristallized from absolute ethanol (60 ml) giving1-[N-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyroyl]-2-pyrrolidinone (7.6g; 88% yield) with m.p. 141°-142° C.

¹ H-NMR (DMSO-d₆): delta (ppm): 1.6-2.3 (4H, m, 2CH₂ --CH₂ --CH₂);2.3-4.0 (8H, m, 2CH₂ N, 2CH₂ CO); 7.41 (1H, s, --CH═).

EXAMPLE 7 N-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyric acid2-amino-2-hydroxymethyl-1,3-propanediol salt (Compound no. 22)

To a solution of N-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyric acid(11.08 g; 0.04 mol), prepared according to the method described inexample 1, in aqueous ethanol at 95% (80 ml),2-amino-2-hydroxymethyl-1,3-propanediol (4.85 g; 0.04 mol) was added andthe solution was stirred for 30 minutes at room temperature. Afterevaporation of the solvent, the solid residue was crystallized fromisopropanol (160 ml) givingN-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyric acid2-amino-2-hydroxymethyl-1,3-propanediol salt (14.8 g; 93% yield) withm.p. 133°-135° C.

¹ H-NMR (DMSO-d₆): delta (ppm): 1.72 (2H, m, CH₂ --CH₂ --CH₂); 2.14 (2H,dd, CH₂ CO); 3.25 (2H, m, N--CH₂); 3.37 (6H, s, 3CH₂ O); 5.73 (6H, broads, exchangeable protons); 7.35 (1H, s, --CH═); 9.39 (1H, t, CONH).

In a similar way the following compound was prepared.

N-(3-bromo-5-isoxazolecarbonyl)-4-aminobutyric acid sodium salt(Compound no. 23)

m.p.>200° C. (ethanol); 87% yield.

¹ H-NMR (D₂ O): delta (ppm): 1.78 (2H, m, CH₂ --CH₂ --CH₂); 2.18 (2H,dd, CH₂ CO); 3.31 (2H, dd, N--CH₂); 7.03 (1H, s, --CH═).

EXAMPLE 8 Pharmacodynamic evaluation: electroshock (ECS) amnesia test inrat

Male rats weighing 130-150 g and fasting for at least 12 hours beforethe beginning of the test were used.

The test consisted in two experiments with a resting interval of 24hours between them.

First experiment: training session

The animals were trained to associate the passage from a light partitionto a dark one, in a suitable box, with a noxious stimulation that is anelectric stimulation through an electrified grid (foot-shock: 1 mA for10 seconds).

Second experiment: retention session

The ability of the animals to remember was evaluated as the timeutilized to repeat the passage through the partitions (retention time).

Evaluation of the retention time in control groups of animals

The test was carried out first on two groups of animals as control.

A first group of rats (hereinafter indicated as control), whichremembered the association between the passage and the noxiousstimulation, showed a conditioned response that led to avoid therepetition of the passage.

A second group of animals (hereinafter indicated as ECS control), whichunderwent a treatment for inducing amnesia (ECS: 90 mA, 100 Hz for 1second) immediately after the training session, showed a decreasedconditioned response and a large number of rats repeated the passage.

Fixing 60 seconds as time-limit for performing the second experiment,the average time (retention time) utilized for the passage was 54seconds for the control and 32 seconds for the ECS control.

Evaluation of the retention time in groups of treated animals

Groups of 20 rats underwent the training session, the treatment forinducing amnesia and the retention session after administration of thecompounds object of the present invention and of the referencecompounds, Piracetam and Aniracetam.

The administration was carried out 30 minutes before the trainingsession in case of intraperitoneal administration (i.p.) and 60 minutesbefore in case of administration by oral route. At least three doseseach compound and each administration route were tested.

The difference between the retention time of the control and theretention time of the ECS control was considered as reference (Δt) andit was fixed, as percentage, equal to 100.

In the groups of animals which were treated and underwent ECS theactivity against amnesia of the compounds object of the presentinvention was expressed as ED₅₀ that is as the dose of compound able togive an improvement of the retention time equal to 50% of the referenceinterval (Δt) in comparison with the ECS control. As example the ED₅₀values of some representatives of the compounds of formula I arereported in table 1.

                  TABLE 1                                                         ______________________________________                                        Compound                                                                      no.        ED.sub.50 i.p. (μmol/kg)                                                                 ED.sub.50 os (μmol/kg)                            ______________________________________                                        1          102           290                                                  2          160           260                                                  3          276           868                                                  4          202           383                                                  8          25            80                                                   12         171           1000                                                 19         --            261                                                  21         --            254                                                  Piracetam  329           1550                                                 Aniracetam 353           1110                                                 ______________________________________                                    

We claim:
 1. A compound of formula ##STR17## wherein n represents anumber selected from 1 and 2;R represents a hydrogen atom, a halogenatom, hydroxy, a C₁ -C₆ alkyl or alkoxy; R₁ represents hydroxy, anoptionally unsaturated C₁ -C₁₈ alkoxy or an ##STR18## group; R₂ and R₃,the same or different, represent a hydrogen atom, a linear or branchedC₁ -C₆ alkyl, or a group of formula

    (CH.sub.2).sub.m R.sub.4

wherein m represents an integer selected from 1, 2 and 3; R₄ representsa carboxy group, an alkoxycarbonyl group having from 1 to 6 carbon atomsin the alkoxy moiety or a group of formula ##STR19## R₅ and R₆, the sameor different, represent a hydrogen atom or a linear or branched C₁ -C₆alkyl; or one of R₂ and R₃ represents a group of formula ##STR20##wherein R₄ has the above meanings and R₇ represents a linear or branchedC₁ -C₄ alkyl optionally substituted by phenyl, hydroxy or by a mercaptogroup, and the other one of R₂ and R₃ represents a hydrogen atom; or inaddition R₂ and R₃, together with the nitrogen atom to which they arebonded, form a heterocyclic selected among the class consisting of1-pyrrolidinyl, 1-piperazinyl, 4-methyl-1-piperazinyl, 1-piperidyl and1-pyrrolidinyl-2-one; and pharmaceutically acceptable salts thereof. 2.A compound, according to claim 1, wherein R represents chlorine,bromine, hydroxy, methoxy, ethoxy, methyl or ethyl.
 3. A compound,according to claim 1 or 2, wherein R₁ represents hydroxy.
 4. Apharmaceutical composition with nootropic activity comprising anootropically effective amount of a compound according to claim 1 or 2together with one or more exipients suitable for pharmaceutical use. 5.A method for the treatment of impairments of cerebral functionality dueto aging as well as to pathologic or traumatic reasons which aretreatable comprising administering a nootropically effective amount of acompound according to claim 1 or
 2. 6. A compound of claim 1 wherein R₁is selected from the group consisting of OCH₃, OC₂ H₅, OC₄ H₉, OC₆ H₁₃,O--CH₂ --(CH₂)₇ --(CH═CH--CH₂) ₃ --CH₃ or --O--CH₂ --(CH₂)₁₄ --CH₃). 7.A compound of claim 1 wherein R₁ is N(R₂) (R₃) and N(R₂) (R₃) isselected from the group consisting of pyrrolidine, 2-pyrrolidinone,piperazine, N-methyl-piperazine, glycine, alanine, valine, serine,cysteine and phenylalanine.